Seems you could do the repair with just your lathe. Cut off the broken top of the pedestal and line bore a stepped area to receive a new top. Remake the top part with a matching stepped section to match the receiver you've bored into the pedestal. Epoxy or braze back together. It's pretty much in compression anyway.

The part that has that chip is part of a ring with those 3 tapped holes. The ring is about 1/4" thick. Then below the ring the wall of the tube is thinner. I would cut down the entire ring section and turn a new ring with a step probably at least 1/4" long. Then you could tack weld the new ring in place and grind the welds down to be flush with the cylinder body. Finish off with body filler, there is no shame in using filler it because a Bridgeport is covered all over with it.

As you can get in from underneath drill out the damaged holes to take a "curved T" headed insert with the stem tapped to take the securing screw. Anoint with suitable glue and push in from underneath then build up the surrounding area with hard filler. Devon or similar metal loaded probably best. J-B weld would work OK if you dammed things so it can't escape whilst setting. Time I did similar fix I just used ordinary body-filler and called it good as there was solid metal, as in this case, bolted on top.

I'd be unsurprised to find that drilling out, filling with Devcon and fitting a helicoil or merely tapping would male a perfectly satisfactory fix. Despite having successfully tapped holes in Devcon it needs a braver, or at least one with better understanding of the strength of metal loaded fillers, than I to try it there tho'.

I was going to say with not even one machine you could flat file the top to square and smooth in the still good places/
Drill and tap three new hole in good places.. fill the empty places with any filler and file smooth to hide and put it back in place. Still plenty strong and would look like new.

And the broken area looks like only a few threads were in use and perhaps so dry they became stuck over time..unsticking may have been resolved with drilling out or soaking but would have been best served with a bit of grease or never seize at the original long past assembly.
Agree most machines were put together with not expecting them to set out in the weather so becoming one solid mass over many years.
I

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